Formation of B-N-C Coordination to Stabilize the Exposed Active Nitrogen Atoms in g-C3N4 for Dramatically Enhanced Photocatalytic Ammonia Synthesis Performance

It is an important issue that exposed active nitrogen atoms (e.g., edge or amino N atoms) in graphitic carbon nitride (g-C3N4) could participate in ammonia (NH3) synthesis during the photocatalytic nitrogen reduction reaction (NRR). Herein, the experimental results in this work demonstrate that the exposed active N atoms in g-C3N4 nanosheets can indeed be hydrogenated and contribute to NH3 synthesis during the visible-light photocatalytic NRR. However, these exposed N atoms can be firmly stabilized through forming B-N-C coordination by means of B-doping in g-C3N4 nanosheets (BCN) with a B-doping content of 13.8 wt%. Moreover, the formed B-N-C coordination in g-C3N4 not only effectively enhances the visible-light harvesting and suppresses the recombination of photogenerated carriers in g-C3N4, but also acts as the catalytic active site for N-2 adsorption, activation, and hydrogenation. Consequently, the as-synthesized BCN exhibits high visible-light-driven photocatalytic NRR activity, affording an NH3 yield rate of 313.9 mu mol g(-1) h(-1), nearly 10 times of that for pristine g-C3N4. This work would be helpful for designing and developing high-efficiency metal-free NRR catalysts for visible-light-driven photocatalytic NH3 synthesis.